Worried about Western jets, Russia is likely to risk its early-warning planes near the front lines to give its formidable S-400s an edge, intel says

• Russia has likely started using its valuable early-warning planes in the Ukraine war, UK intel said.
• British intelligence said Moscow might be worried about Kyiv deploying Western fighter jets.

Russia has likely started using its valuable early-warning planes in its war in Ukraine to give its air defenses a boost, indicating Moscow may be worried about Kyiv deploying Western fighter jets in the near future, Western intelligence said.

The UK's Defense Ministry wrote in a Friday intelligence update that Russia was thought to have deployed its A-50 Mainstay D aircraft to identify targets over Ukraine for its prized SA-21 long-range ground-based air-defense missile system, more commonly known by its Russian name: the S-400 Triumf.

"This adds to Mainstay's core mission of co-ordinating fighter aircraft," the intelligence update said.

British intelligence added that the A-50 Mainstay aircraft had the ability to use its sophisticated radar to spot enemy planes at longer ranges because "its altitude allows it to see further around the curvature of the Earth," while the S-400 radars were more limited.

Russia has "likely expedited integrating" the Mainstay and S-400 "partially because it is concerned about the prospect of Ukraine deploying Western-provided combat aircraft," the British update said.

Britain said there's a "realistic possibility" that Russia would "accept more risk" by flying the early-warning aircraft closer to the sprawling front line that stretches across Ukraine "to effectively carry out its new role."

The trade-off for Moscow is that this could put the plane within range of Ukraine's air defenses, which have largely kept the Russian air force at bay.

As an airborne early-warning and control aircraft, the Mainstay — NATO's name for the decades-old Soviet-era Beriev A-50 — can detect inbound threats such as aircraft and missiles. It can also act as a mobile command and control center, miles above the battlefield, and direct air engagement and strikes.

Because they can fly at high altitudes and are very mobile, these planes also tend to be less vulnerable to attacks than ground-based radars.

While the Mainstay has the capacity to give Russian surface-to-air missile systems more reach, Moscow's formidable S-400 air-defense system has gained significant notoriety in Ukraine and the West for its effectiveness during the war.

The mobile system is capable of engaging targets — including cruise and ballistic missiles and aircraft and drones — at high altitudes and long ranges, and it's considered to be the equivalent of the US military's Patriot system, which Ukraine also operates.

Any concern Russia may have over Western fighter jets comes as Ukrainian pilots and personnel train on how to fly and maintain American-made F-16 fighter jets. Though the much-anticipated program, taking place in both the US and Europe, is underway, some US officials have suggested that Kyiv won't receive the advanced warplanes until next year.

When the fighter jets eventually start flying above the battlefield, how they're used may depend on which missiles the aircraft are equipped with, experts say. In a defensive counterair role, the jets could engage enemy targets including missiles and drones to protect Ukrainian civilians and troops, complementing Kyiv's strained air-defense network, which consists of Western and Soviet-era systems.

In an offensive role, the F-16s could help with air-to-ground operations or engage in the suppression of Russia's air defense. But in any capacity, Britain's intelligence update suggests that Moscow is turning to the Mainstay as a preemptive measure to counter the American warplanes and the threats that they may pose when they arrive.